Orthogonal Frequency Division Multiplexing (OFDM) is a widely used technology in fourth generation wireless networks (4G), 802.11a/g/n WLANs and other communication systems that achieve high transmission rates over dispersive channels by transmitting serial information through multiple parallel carriers. In OFDM, the transmission bandwidth is divided into many narrow sub-channels, which are transmitted in parallel, such that the fading experienced by each channel is flat.
Many applications require that information be communicated in a timely manner, so reliability of these networks is of concern. Various techniques are known in the art for improving transmission reliability and speed. Network coding techniques for OFDM are known in the art, wherein packets are combined and transmitted through different nodes or locations to improve the reliability of the channel. These network coding techniques may be employed at the symbol level or the packet level and may include network coding in the MAC (media access control) layer and network coding in the PHY (physical) layer. Additional techniques may include rate diverse network coding, zero cost retransmission and CodePlay.
The prior art methods utilizing network coding are typically applied to two-hop communication systems through a relay and to multicast systems, where it has been proven that network coding provides throughput gain. However, these network coding techniques for OFDM require rerouting of lost data or require a feedback channel from the transmitter to recover lost information.
Accordingly, what is needed in the art is an OFDM based system having improved spectral efficiency, excellent transmission rates, improved throughput, improved performance during multipath fading and the ability to easily retrieve lost information without the need for retransmission or feedback from the transmitter.